Certain standards are currently being drawn up to standardise the transmission of information from an interrogator system to portable objects such as radio frequency tags. These standards or draft standards generally recommend carrier wave amplitude modulation for certain time intervals coupled with positional coding of the intervals; however the techniques defined in these standards cause certain problems, notably in detecting the interval positions. They also create difficulties when tags operate asynchronously, i.e. contain their own local oscillator that operates independently of the carrier wave frequency.
The aim of the present invention is to solve precisely these problems.